Brain receptor autoradiography with [3H]-YM 09151-2: a ligand for labeling dopamine D-2 receptors

Temporal changes of dopaminergic and glutamatergic receptors in 6-hydroxydopamine-treated rat brain

Quantitative receptor autoradiography was used to examine the sequential patterns of changes in dopaminergic and glutamatergic receptors in the brain of rats lesioned with 6-hydroxydopamine. The animals were unilaterally lesioned in the medial forebrain bundle and the brains were analyzed at 1, 2, 4 and 8 weeks of postlesion. Degeneration of the nigrostriatal pathway caused a significant increase in dopamine D(2) receptors in the ipsilateral striatum from 1 to 8 weeks of postlesion. In the ipsilateral substantia nigra (SN), a significant decrease in dopamine D(2) receptors was also observed from 1 to 8 weeks of postlesion. On the other hand, dopamine D(1) receptors were increased in the ipsilateral ventromedial striatum from 2 to 4 weeks of postlesion. In the ipsilateral SN, a transient increase in dopamine D(1) receptors was observed only 1 week after lesioning. However, other regions in both ipsilateral and contralateral sides showed no significant change in dopamine D(1) and D(2) receptors during postlesion except for a transient change in a few regions. N-Methyl-D-aspartate (NMDA) receptors showed no significant changes in all brain regions studied during the postlesion. In contrast, a transient increase in excitatory amino acid transport sites was observed only in the frontal cortex and ventromedial striatum of the ipsilateral side at 2 weeks of postlesion. However, glycine receptors showed a significant change in any brain areas of both ipsilateral and contralateral sides after lesioning. The change in the brain areas of contralateral side was more pronounced than that of ipsilateral side for glycine receptors. In addition, dopamine uptake sites showed a severe damage in the ipsilateral striatum from 1 to 8 weeks after lesioning. In the contralateral side, in contrast, no significant change in dopamine uptake sites was found in the striatum during the postlesion. These results indicate that unilateral injection of 6-hydroxydopamine in the medial forebrain bundle can cause a significant increase in dopamine D(1) and D(2) receptors in the striatum. The increase in dopamine D(2) receptors was more pronounced than that in dopamine D(1) receptors in the striatum after 6-hydroxydopamine treatment. In contrast, dopamine uptake sites showed a severe damage in the striatum during the postlesion. Furthermore, our results support the existence of dopamine D(2) receptors on the neurons of SN, but not dopamine D(1) receptors. For glutamatergic receptor system, the present study suggests that the changes in glycine receptors may be more susceptible to degeneration of nigrostriatal pathway than NMDA receptors and excitatory amino acid transport sites. Thus, our findings are of interest in relation of degeneration of the nigrostriatal pathway that occurs in Parkinson's disease

Quantitative ex vivo and in vitro receptor autoradiography using 11C-labeled ligands and an imaging plate: a study with a dopamine D2-like receptor ligand [11C]nemonapride

Ex vivo and in vitro autoradiography (ARG) with radioluminography is a useful technique to characterize newly developed 11C-labeled positron emission tomography (PET) tracers and to apply them to biological and pharmacological studies. In this report, we have described a method of evaluating the radioactivity distribution quantitatively in ex vivo and in vitro ARG using imaging plates and a dopamine D2-like receptor ligand [11C]nemonapride as a model compound. The photo-stimulated luminescence (PSL) values of the rat brain section provided by the imaging plates showed an excellent linear relationship with the radioactivity in a wide range under constant slice-thickness, although the PSL values slightly decreased with increasing slice-thickness both in ex vivo and in vitro ARG. The injection dose of 11C-tracers for ex vivo ARG was also discussed. We found saturable binding sites of [11C]nemonapride in the cortex besides the striatum both ex vivo and in vitro.

Sequential changes of dopaminergic receptors in the rat brain after 6-hydroxydopamine lesions of the medial forebrain bundle

We investigated the sequential patterns of changes in dopamine uptake sites, D1 and D2 receptors in the brain of animals lesioned with 6-hydroxydopamine using quantitative receptor autoradiography. The rats were unilaterally lesioned in the medial forebrain bundle and the brains were analyzed at 1, 2, 4 and 8 weeks postlesion. Degeneration of the nigrostriatal pathway caused a significant loss of dopamine uptake sites in the ipsilateral striatum, substantia nigra (SN) and ventral tegmental area (VTA) in the lesioned animals. Dopamine D1 receptors were significantly increased in the ventromedial part of striatum of the ipsilateral side from 2 to 4 weeks postlesion. In the ipsilateral SN, a transient increase in dopamine D1 receptors was observed only 1 week after lesioning. However, the frontal cortex, parietal cortex and dorsolateral part of the striatum showed no significant change in dopamine D1 receptors throughout the experiments. On the other hand, dopamine D2 receptors were decreased increased in the ipsilateral SN and VTA from 1 week to 8 weeks postlesion. In the ipsilateral striatum, dopamine D2 receptors were increased in the dorsolateral part from 2 weeks to 8 weeks and in the ventromedial part from 2 weeks to 4 weeks. However, the frontal cortex and parietal cortex showed no significant change in dopamine D2 receptors during postlesion. In the contralateral side, most of regions examined showed no significant change in dopamine uptake sites, dopamine D1 receptors and dopamine D2 receptors during postlesion except for a transient change in a few regions. These results demonstrate that 6-hydroxydopamine can cause a severe functional damage in dopamine uptake sites in the striatum, SN and VTA. Our findings also suggest that the up-regulation in dopamine D2 receptors is more pronounced than that in dopamine D1 receptors in the brain after 6-hydroxydopamine treatment. Furthermore, our results support the existence of dopamine D2 receptors on the neurons of SN and VTA. Thus, our findings provide insights into the pathogenesis of Parkinson's disease.

Ontogeny of human brain dopamine receptors. I. Differential expression of [3H]-SCH23390 and [3H]-YM09151-2 specific binding

Dopamine receptor expression in human fetal forebrain (between 6 and 20 weeks of gestation) was measured using tissue-slice receptor autoradiography with the D1-like and D2-like antagonists [3H]-SCH23390 and [3H]-YM09151-2, respectively. Tissue sections were assayed in saturation studies and examined for age- and sex-related changes in Bmax. We made the following observations: (1) the ages at which D1- and D2-like receptors were first expressed in whole forebrain sections could be reliably identified but were not significantly different from one another (gestational age 65 days for D1- vs. 72 days for D2-like receptors); (2) age-related increases in both D1- and D2-like receptors were demonstrated in forebrain and, from the middle of the first to the middle of the second trimester, the Bmax for each ligand increased by an order of magnitude after the onset of the specific binding site's expression; (3) age-related increases in D1-like receptors, but not D2-like receptors, could be demonstrated in cortex; and, (4) in one case of trisomy 18, the Bmax for [3H]-SCH23390 was significantly elevated above the 95% confidence interval when compared to an age-regressed normal sample. Although D2-like receptor density significantly increased with age in forebrain, age-regressed changes in D2-like receptor expression in cortex and striatum did not reach statistical significance. Likewise, a comparison of the mean Bmax's by sex for both ligands in midgestational striatum failed to reach significance. These data corroborate the findings of other investigators who have delineated the ontogeny of dopaminergic systems in other animal species. The regional differences in the expression of dopamine receptor families may be relevant to the role which dopamine may play during normal gestational brain development. Moreover, significant deviations in dopamine receptor expression during gestation (as seen in this one case of trisomy 18) may signify underlying pathological processes that ultimately are manifested by abnormal psychological development and/or cognitive functioning.

Effect of cerebral ischemia on dopamine receptors and uptake sites in the gerbil hippocampus

Dopamine D1 and D2 receptors and uptake sites were studied in the gerbil hippocampus, parietal cortex and thalamus 1 h to 7 days after 10 min of cerebral ischemia using the occlusion of bilateral common carotid arteries. [3H]SCH23390 ([N-methyl-3H]R[+]-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-7-ol-be nzazepine) and [3H]mazindol were used as markers of dopamine D1 receptors and uptake sites, respectively. [3H]Nemonapride was used to label dopamine D2 receptors. No obvious alteration in [3H]SCH23390 and [3H]mazindol binding was found in the hippocampus up to 48 h after ischemia. These bindings showed a significant reduction in the hippocampus after 7 days of recirculation. In contrast, [3H]nemonapride binding was unaffected in the hippocampus during the recirculation periods. The parietal cortex and thalamus also exhibited no significant changes in [3H]SCH23390, [3H]nemonapride and [3H]mazindol binding after ischemia. MAP2 (microtubule-associated protein 2) immunoreactivity was unchanged in all regions up to 48 h after ischemia. Thereafter, a marked loss of MAP2-immunoreactive neurons was observed in the hippocampal CA1 and CA3 neurons 7 days after recirculation. These findings were consistent with histological observations with cresyl violet staining. Our results demonstrate that dopamine D1 receptors and dopamine uptake sites in the hippocampus are susceptible to cerebral ischemia, whereas dopamine D2 receptors in this region are particularly resistant. Furthermore, these findings suggest that dopamine transmission may not be major factor in producing ischemic hippocampal damage.

Effect of aging on dopaminergic receptors and uptake sites in the rat brain studied by receptor autoradiography

We studied the age-related alterations of dopaminergic receptors in the brain of Fisher 344 rats with various age (3 weeks and 6, 12, 18 and 24 months) using in vitro receptor autoradiography. [3H]SCH 23390, [3H]spiperone and [3H]nemonapride, and [3H]mazindol were used to label dopamine D1 receptors, dopamine D2 receptors and dopamine uptake sites, respectively. In immature rats (3 weeks old), [3H]SCH 23390 binding showed a significant increase in most brain regions compared to adult animals (6 months old), whereas [3H]spiperone and [3H]nemonapride bindings showed no significant alteration in any brain areas. In contrast, [3H]mazindol binding showed a significant decline in most brain regions. On the other hand, the age-related alterations in [3H]SCH 23390 binding were not observed in any brain regions. [3H]Spiperone and [3H]nemonapride bindings also showed no significant alteration in the brain during aging, except for a transient alteration in [3H]spiperone binding in the nucleus accumbens and hippocampus of 12 months old rats. However, [3H]mazindol binding showed a significant reduction in most brain areas of 12 months old rats. Thereafter, the age-related reduction in [3H]mazindol binding was observed in most brain regions of 18 and 24 months old rats. The results demonstrate that dopamine uptake sites are more susceptible to the aging process than both dopamine D1 and D2 receptors. Furthermore, our results suggest that dopaminergic receptors and dopamine uptake sites may develop with different patterns and speeds after birth. Our studies may provide valuable information concerning the effect of aging on dopaminergic systems.

Effects of cerebral ischemia on dopamine receptors in the gerbil striatum

Dopamine D1 and D2 receptors and uptake sites were studied in the gerbil striatum and frontal cortex 1 h to 7 days after 10 min of cerebral ischemia caused by occlusion of the bilateral common carotid arteries. [3H]SCH23390 ([N-methyl-3H]R[+]-8-chloro-2, 3,4,5-tetrahydro-3-methyl-5-phenyl-7-ol-benzazepine), [3H]nemonapride and [3H]mazindol were used as markers of dopamine D1 receptors, D2 receptors and uptake sites, respectively. A significant reduction in [3H] SCH23390 binding was found in the striatum from 48 h after ischemia. In contrast, during the recirculation periods, [3H]nemonapride and [3H]mazindol binding was mostly unaffected in this region which was the most vulnerable to ischemia. The frontal cortex, where ischemic neuronal damage was mild, also showed no significant changes in [3H]SCH23390, [3H]nemonapride and [3H]mazindol binding after ischemia. Thus, cerebral ischemia that was associated with cell loss in the striatum resulted in a selective reduction of dopamine D1 receptors and not D2 receptors. No changes in dopamine D1 or D2 receptors were observed in frontal cortex. If massive dopamine release occurs with cerebral ischemia, it is not reflected by modification in the number of uptake sites located on dopamine terminals.

Effects of 6-hydroxydopamine lesions of the medial prefrontal cortex on local cerebral blood flow and D1 and D2 dopamine receptor binding in rats: a quantitative autoradiographic study

The effects of lesions of the dopamine (DA) nerve terminals in the medial prefrontal cortex (MPFC) on local cerebral blood flow (LCBF) and DA receptor binding in rats were investigated. 4 micrograms of 6-hydroxydopamine (6-OHDA) was infused stereotaxically into the area of the bilateral MPFC of rats pretreated with desmethylimipramine, and control rats received a vehicle solution. Twenty-four days after the operation LCBFs of 23 brain regions were measured using the quantitative autoradiographic N-isopropyl-p-[125I]iodoamphetamine technique D1 and D2 DA receptor binding in various brain regions was also quantified autoradiographically using [3H]SCH 23390 and [3H]YM 09151-2 as the respective ligands. 6-OHDA lesions of MPFC produced significant increases in LCBF of the nucleus accumbens, the dorsolateral portion of the caudate-putamen and the anterior cingulate cortex. The lesioned animals did not show decreased LCBF in MPFC per se. D1 and D2 DA receptor binding was not affected in any brain region examined. These results suggest that lesions of the DA nerve terminals in MPFC induce an enhancement of functional activity in the terminal regions of the subcortical DA systems, and that hypofunction of the mesocortical dopamine system does not elicit reduced metabolic activity in the prefrontal cortex.

Dopamine D2-like receptors labeled by [3H]YM-09151-2 in the rat hippocampus: characterization and autoradiographic distribution

Dopamine D2-like receptor labeled by [3H]YM-09151-2 in the rat hippocampus proper was examined by in vitro receptor autoradiography. In the dorsal hippocampus, [3H]YM-09151-2 bindings were high in the whole layers of CA1, the stratum pyramidale of CA4 and the stratum molecular of gyrus dentatus, moderate in the stratum oriens of CA3 and hilus of the gyrus dentatus, and low in remaining CA3 and the subiculum. In the ventral hippocampus, the binding densities were high in the stratum oriens and the stratum radiatum of CA1, the stratum pyramidale of CA4, and the stratum moleculare of gyrus dentatus, moderate in the stratum lacnosum moleculare of CA1 and the hilus of the gyrus dentatus. Saturation analysis using hippocampal sections demonstrated that the Kd value was about five times higher than that using striatal sections. The rank order potency of competition on [3H]YM-09151-2 binding by dopaminergic ligands in the hippocampus was YM-09151-2 > (+)-butaclamol > dopamine > sulpiride > SCH-23390; which shows the appropriate dopamine D2-like receptor profile. The hippocampal [3H]YM-09151-2 binding did not represent serotonergic receptors (5-HT1A and 5-HT2) and sigma receptor, since Ki values of ketanserine, serotonin, 8-OH-DPAT and DTG were much lower than D2-like receptor antagonists. These findings suggest tha [3H]YM-09151-2 binds hippocampal D2-like receptor site with different association kinetics of striatal D2-like receptor site, and demonstrates widespread distribution of D2-like receptor in the hippocampus with distinct region-specific profile.

Localization of high affinity [3H]glibenclamide binding sites within the substantia nigra zona reticulata of the rat brain

The rat substantia nigra zona reticulata contains a high density of binding sites for glibenclamide, an adenosine triphosphate-sensitive potassium channel inhibitor, but the precise location of glibenclamide binding sites within this area has not previously been examined. By combining neurochemical lesion and autoradiographical studies we have shown that high affinity [3H]glibenclamide binding sites are located on striatonigral terminals. Unilateral injections of 6-hydroxydopamine into the medial forebrain bundle or of quinolinic acid into the striatum were performed in anaesthetized adult rats to lesion the nigrostriatal and striatonigral pathways respectively. Autoradiography was performed on coronal sections of midbrain with [3H]glibenclamide, [3H]YM-09151-2 (dopamine D2 receptor antagonist) and [3H]SCH 23390 (dopamine D1 receptor antagonist) at three rostrocaudal levels of the substantia nigra. Under the conditions of the incubation [3H]glibenclamide binds primarily to the high affinity site. Following the 6-hydroxydopamine nigrostriatal lesion, D2 receptor binding was reduced (by up to 67%) on the lesioned side at all three levels of the substantia nigra whereas D1 receptor and glibenclamide binding were not significantly affected. In contrast, following striatonigral pathway lesion with quinolinic acid D2 receptor binding was unchanged on the lesioned side, but both D1 receptor and glibenclamide binding were reduced at all three levels (by up to 85% and 63% in the area of maximum lesion, respectively). In adjacent sections, the pattern of D1 binding loss was closely paralleled by the loss of glibenclamide binding. These results demonstrate that the high affinity glibenclamide binding sites of the substantia nigra zona reticulata are, at least in part, located on the terminals of striatonigral projection neurons.

Ontogeny of [3H]-SCH23390 and [3H]-YM09151-2 binding sites in human fetal forebrain

In order to determine the gestational age at which binding sites for the dopamine "D1-like" and "D2-like" receptor antagonists, [3H]-SCH23390 and [3H]-YM09151-2, respectively, can be reliably detected in the human and to identify any discrete anatomic distribution of these binding sites, fetal forebrain tissue sections from mid-first (n = 4) and mid-second (n = 4) trimester gestations were used for receptor autoradiography. Specific binding for both ligands was detectable at the earliest fetal age examined (gestational week 6). Age-related increases in maximum saturation binding were demonstrated for both ligands using tissue sections from basal forebrain. The Bmax for both [3H]-SCH23390 and [3H]-YM09151-2 binding increased ten-fold comparing gestational week 6 and gestational week 18 values. In the cortex at gestational day 120, [3H]-YM09151-2 specific binding could be seen at the gray-white matter boundary, which was more prominent by gestational day 140. In contrast, [3H]-SCH23390 specific binding to the cortex at gestational day 120 did not appear to differentiate specific areas and did not increase between gestational days 120 and 140. These preliminary observations in human fetal brain provide evidence that dopamine "D2-like" binding sites can be localized in a discrete cortical area in the course of normal human brain development. Characterizing these binding sites and the population of cells that demonstrates these binding sites may be relevant to neurodevelopmental hypotheses of psychiatric disorders.

Nicotine induced c-fos expression in the striatum is mediated mostly by dopamine D1 receptor and is dependent on NMDA stimulation

The powerful psychostimulant and positive reinforcing effects of nicotine have been speculated to be mediated by the dopaminergic neurons of the ventral tegemental area (VTA) and their terminals in the nucleus accumbens. To extend our understanding of nicotine and dopamine interactions, we mapped the pattern of c-fos expression in the striatum as an important marker of some of the earliest changes that occur at gene transcription level. Acute nicotine injections in rats led to Fos expression more prominently in the caudatoputamen than in the nucleus accumbens in a dose-dependent fashion. Fos-reactive cells were more prominent in the central and dorsomedial limbic caudatoputamen than in the dorsolateral sensory-motor striatum. Injections of mecamylamine completely blocked nicotine-induced Fos expression. Injections of the selective dopamine D1 antagonist SCH 23390, but not D2 antagonist YM 09151-2 or Clozapine, a drug with high affinity to D4 receptors, before nicotine injections, completely blocked Fos expression in the striatum. Nicotine induced Fos expression was also blocked completely by the NMDA receptor antagonists MK-801 and CPP. These results suggest that nicotine-induced Fos expression in the striatum is mediated mostly by dopamine D1 receptors and that the Fos expression is also dependent on N-methyl-D-aspartate (NMDA) stimulation.

Dopamine D3 receptor mRNA and binding sites in human brain

Dopamine D3 receptors (Sokoloff et al., 1990) have been shown to be related to dopamine D2 receptors and have been suggested to play a role in mediating the antipsychotic effects of neuroleptics. So far studies on the expression of D3 mRNA and of binding sites with pharmacological characteristics of D3 receptors have been restricted to rat brain. Using in situ hybridization histochemistry, we demonstrate that D3 mRNAs are enriched in human n, accumbens and in the islands of Calleja. In addition, D3 mRNA was detected at very low levels in anterior caudate and putamen with a rostro-caudally decreasing gradient and in hypothalamic mammillary nuclei. In receptor autoradiographic binding studies, the islands of Calleja were found to be labeled by [125I]iodosulpride and [3H]CV 205 502 but not by [3H]raclopride and [3H]YM 09151-2. Pharmacological analysis of binding of the D2/D3 ligand [3H]CV 205 502 in n. accumbens and caudate-putamen is consistent with the presence of D3 receptor sites in ventral striatum. Overall distribution and pharmacology of D3 sites in human and rat brain appear to be similar. Presence and distribution of D3 receptors in human brain are compatible with the notion that D3 receptors might be involved in mediating the clinical effects of antipsychotics.

Differential visualization of dopamine D2 and D3 receptor sites in rat brain. A comparative study using in situ hybridization histochemistry and ligand binding autoradiography

At least five members of the dopamine receptor family have been characterized at the gene level. D2, D3 and D4 dopamine receptors are related pharmacologically. In order to visualize the differential expression of D1, D2 and D3 receptors in rat brain we have combined in situ hybridization histochemistry with receptor autoradiography. Regions enriched with D3 messenger RNA (mRNA) included the islands of Calleja (ioC) and nucleus accumbens. Very low or undetectable levels were present in the caudate-putamen. In contrast, no D2 transcripts were observed in the islands of Calleja, but there were high levels in the nucleus accumbens, caudate-putamen (CP) and pyramidal layer of the olfactory tubercle. A comparison of the binding pattern of six dopamine receptor radioligands hitherto regarded as D2 receptor-selective showed that the islands of Calleja were intensely labelled by [125I]iodosulpride, [3H]CV 205 502 and [3H]SDZ 205 501, while the binding of [3H]spiperone, [3H]raclopride and [3H]YM 09151-2 was much lower or undetectable. Pharmacological analysis of the binding of D2/D3 ligands to the islands of Calleja and caudate-putamen suggests that binding sites in these two regions are of different pharmacology, consistent with the presence of D3 sites in the islands of Calleja and the predominance of D2 sites in the caudate. These results demonstrate the expression of D3 binding sites in the rat brain and provide a procedure to differentiate D2 and D3 receptor populations in binding studies.

The cloned dopamine D2 receptor reveals different densities for dopamine receptor antagonist ligands. Implications for human brain positron emission tomography

Since [3H]emonapride ([3H]YM-09151-2), a benzamide neuroleptic, consistently detects more dopamine D2 receptors than [3H]spiperone in the same tissue, we tested whether this property was inherent in the cloned dopamine D2 receptor. We found that the density of dopamine D2 receptors labelled by [3H]emonapride was 1.5-fold to 2-fold (mean of 1.8-fold) higher than the density of dopamine D2 receptors labelled by [3H]spiperone in cells expressing cloned dopamine D2 receptors (either the short form (from rat) or the long form (from human)), matching similar findings in anterior pituitary tissue (rat or pig) or in post-mortem human caudate nucleus tissue. The situation was similar for another benzamide, [3H]raclopride, which revealed 1.3-fold to 1.8-fold (mean of 1.5-fold) more binding sites than that for [3H]spiperone in cell membranes containing cloned dopamine D2 receptors. The apparently different dopamine D2 receptor densities revealed by these two types of 3H-ligands (i.e. [3H]spiperone and the [3H]benzamides), therefore, arise from an inherent property of the dopamine D2 receptor protein. These findings for the cloned dopamine D2 receptor, therefore, partly explain the higher dopamine D2 receptor density measured in human brain (by positron emission tomography) when using radioactive raclopride compared to results using radioactive methylspiperone.(ABSTRACT TRUNCATED AT 250 WORDS)